Production of motor fuels from heavy hydrocarbon oils in a two stage conversion process with inert solids



E. ADAMS ET AL 2,690,990 PRODUCTION OF MOTOR FUELS FROM HEAVY HYDROCARBON OILS NVERSION PROCESS WITH INERT SOLIDS cw E G A T s 0 W T A Mm 9 H 5 .8 C U 3 Sheets-Sheet 1 Filed Sept. 8, 1950 PIZODUCT m U Q U L A T O T- M w w GASOLINE CARBON WT.

950 I000 on'r me 'TEMPEQA UQE, F.

Fla-1 clarle E. Adams attorney Oct. 5, 1954 Filed Sept. 8, 1950 C. E. ADAMS ET AL 2,690,990 PRODUCTION OF MOTOR FUELS FROM HEAVY HYDROCARBON OILS IN A TWO STAGE CONVERSION PROCESS WITH INERT SOLIDS 3 Sheets-Sheet 2 larfz, [5 Adams as I0. Kimberlin.

I 5 m 457 FI Q.

JnBnvenbors am d Mat. of

Clc'ocirneg C. E. ADAMS ET AL Oct. 5, 1954 2,690,990 PRODUCTION OF MOTOR FUELS FROM HEAVY HYDROCARBON OILS IN A TWO STAGE CONVERSION PROCESS WITH INERT SOLIDS Filed Sept. 8, 1950 3 Sheets-Sheet 3 v @6 x i dab/mu P wwm 1 I Q m a m y .:\\l\||||fl\ llllq Z a r m JQOJUYU (I w rqclmllll m mm m Q Al 0 55 F Al \mm k mwim 0200mm P :1 m ml... mdjom SE93 2 6m. Nu o hT xuzma @2525. MN. 2 J mnfl ruzmna www mk m l0 mojom SE05: mfl.\ wb V E. MC Irv mim mo cl s lmfi rzm. Jr. EJn-ve nbor'S Qtt 0.34

CLbtorne. 51W :5

Patented Oct. 5, 1954 PRODUCTION OF MOTOR FUELS FROM HEAVY HYDROCARBON OILS IN A TWO STAGE CONVERSION PROCESS WITH INERT SOLIDS Clark E. Adams, Charles N. Kimberlin, Jr., and William J. Mattox, Baton Rouge, La., assignors to Standard Oil Development Company, a corporation of Delaware Application September 8, 1950, Serial No. 183,828

11 Claims. 1

The present invention relates to a process of treating hydrocarbons. More particularly, the invention pertains to a method of producing from high-boiling hydrocarbon oils of the type of topped or reduced crude or similar heavy residues increased quantities of motor fuel range fractions as well as higher boiling distillate fractions suitable for further cracking. Broadly, the invention involves the coking of heavy residues of the type mentioned above in two stages wherein the feed is first contacted with hot fluidized inert solids at relatively mild coking conditions, particularly at relatively low temperatures, to crack the more readily cracked feed constituents into product vapors, gases and coke and to disperse the more refractory components on the inert solids, while in the second stage the inert solids carrying the more refractory components are subjected in fluid operation to more severe cracking conditions, particularly to relatively high temperatures, to produce additional amounts of product vapors, gases and coke.

In conventional petroleum refining the crude petroleum is first distilled to produce various distillate fractions and a residue boiling above about 700 F. Motor fuels are normally produced from the distillate fractions by suitable refining processes including thermal or catalytic cracking, reforming, isomerization, alkylation, etc., while the residue is worked up to yield marketable highmolecular weight products, such as lubricating oils, waxes, asphalt, fuel oils, etc. More recently, however, the demand for motor fuels has increased so greatly that it has become desirable to use the residues from the crude distillation extensively as an additional source of motor fuels.

It has been known for a long time that motor fuels may be produced by coking crude residua, that is by subjecting the residues to cracking at severe conditions including relatively high temperatures and long holding times. The use of cracking catalysts in this reaction has likewise been proposed. However, serious difiiculties have been encountered in th catalytic type of operation chiefly as the result of the high ash content of the feed and the high rate of coke formation. Aside from the fact that the heavy coke deposits in the coking vessels and transfer lines require frequent cleaning periods and plant shut-downs, catalyst contamination and deactivation by coke and difficultly removable ash constituents of the feed is so rapid that crude residua have been considered highly undesirable as feed stocks for catalytic cracking processes. Furthermore, in

cracking reduced crudes or the like it is desirable to preheat the feed to a temperature considerably below that at which any appreciable coking will occur. Thereafter, the feed is contacted with sufficient hot catalyst to give the resulting mixture the temperature desired for the cracking operation. Because of the large amounts of heat required for these purposes, large amounts of hot catalyst must be used to supply the required heat or smaller amounts of catalyst must be heated to a very high temperature. Neither operation is desirable.

Some of these difficulties may be avoided in accordance with prior suggestions by coking residues in a dense, turbulent bed of hot subdivided catalytically inert solids, such as coke, pumice, kieselguhr, spent clay, sand, or the like fluidized by upwardly flowing gases or vapors. These solids serve primarily as a carrier for the coke formed and as a scouring agent preventing coke deposition on equipment walls. Also gasoline yields are higher as a result of the high surface area of the solids. The coke deposited on the solids may be burnt off in a separate fluid type heater vessel from which hot solids may be returned to supply heat required for coking. It is a matter of record that fluid operation affords greatest advantages with respect to heat transfer and economy, temperature control, ease and continuity of operation, etc.

While procedures of this type avoid catalyst contamination and heat supply by circulation of catalyst as well as difficulties resulting from coke deposition on equipment walls, they have been found deficient with respect to ease of fluidization as well as in the relative proportions of volatile products and coke formed. When it is attempted to carry out a fluid coking operation of this type at severe cracking conditions conducive to the formation of maximum amounts of volatile products, the formation of coke and extremely heavy refractory hydrocarbonaceous material is so rapid that a caking of the fluidized solids takes place whereby large agglomerates of solids are formed which destroy the fluid character of the bed. When milder conditions are employed in order to reduce the rate of coke formation, a reduction in the yield of total product vapors results and the proportion of motor fuel range hydrocarbons in the volatile product drops off sharply. The present invention overcomes this difliculty.

It is, therefore, the principal object of the present invention to provide improved means for producing motor fuels and high boiling distillate fractions by coking heavy oil residues in contact with fluidized, inert solids. Other and more specific objects and advantages will appear from the description of the invention given below wherein reference will be made to the accompanying drawing wherein Figure 1 is a graphical illustration of experimental data demonstrating the effects of a preferred embodiment of the invention; and

Figures 2 and 3 are schematical illustrations of systems suitable to carry out specific embodiments of the invention.

It has now been found that coke formation may be controlled so as to establich optimum fluidization characteristics of the fluidized solids at maximum yields of Volatile products when the coking of heavy residues on fluidized inert solids is carried out in two stages maintained at diiferent conditions. More specifically, the oil feed is first contacted at relatively mild coking conditions,

particularly at a relatively low temperature, with a. dense, turbulent, fluidized mass of catalytically inert solids to produce volatile products, coke and materials involatile or not crackable at these mild conditions. Volatile products are withdrawn from this stage while the coke and the involatile or refractory materials are deposited and dispersed on the inert solids. The inert solids carrying the coke and involatile or refractory materials are passed to the second stage wherein they are subjected in the form of a turbulent fluidized mass of solids to relatively severe coking conditions, particularly a relatively high temperature, conducive to complete cracking of the most refractory feed constituents, resulting in the formation of additional quantities of volatile, cracked products and coke. At least a portion or all of the volatile products formed in the first stage may be contacted with the inert solids of the second stage substantially at the higher temperature of the second stage to improve the ratio of motor fuel range hydrocarbons over higher boiling volatile products in the efiiuent of the first stage. Heat required in the coking stages is supplied by circulating a stream of inert solids between the coking stages and a fluid type heating zone wherein the inert solids are reheated in the fluidized state by combustion of coke deposited on the inert solids during the coking operation.

"When so operating, the easily cracked feed components are converted to coke of relatively high hydrogen content and volatile products in the first stage The coke so formed is capable of yielding additional volatile products upon heat ing to the higher temperature of the second stage.

This coke, together with the uncracked hydrocarbonaceous residue of the feed, may be readily absorbed by the fluidized solids in the first coking stage without caking of the solids. In the second stage, this coke is reduced in hydrogen content with the formation of additional volatile products. Also, in the second stage, coke formation results from the further cracking of the highly refractory feed components evenly dispersed on the inert particles whereby the danger of caking is avoided in this stage. In other words, caking and fluidization troubles are eliminated by spreading the deposition of materials which may cause caking over the total contact time of two fluid contacting stages, each operated at conditions suitable to depress the rate of deposition far below that encountered in single stage operation, involving maximum conversion into volatile products.

For the purposes described above, the temperature in the first stage should be maintained within the approximate range of 800-950 F., preferably at about 850-950 F. The solids residence time in this stage should not exceed about 20 minutes and is preferably maintained within the range of about /2-5 minutes to avoid caking and loss of fluidity. In order further to inhibit caking, the volume of the fluidized solids bed in the first stage should not be less than and preferably should be at least the volume of liquid residue supplied to the first stage per hour. The temperature in the second stage should be maintained at about 900-1150 F., preferably at about 950-1100 F. The residence time of the coke in this high temperature stage is less critical than in the first stage; it should exceed, however, 5 minutes and it is preferably maintained at about 20 minutes. The inert solids useful for the purposes of the invention include coke from petroleum or coal, sand, pumice, spent clays, etc. Certain catalytic solids may also be used, such as activated clays or synthetic composites of the silica-alumina type. These solids may have a particle size of about -500 microns, preferably about -200 microns.

Two stage operation in accordance with the invention affords optimum product distribution in favor of motor fuel production at the expense of higher boiling volatile products and at relatively low coke formation. Experimental data indicate that in coking oil residues on inert fluidized solids, coke formation and gasoline yield decrease and the gas oil yield increases as the coking temperature increases within the range of about 850- 950 F. while at temperatures above about 950 F. a further increase of temperature increases the gasoline yield at the expense of the gas oil yield without appreciably affecting the rate of coke formation. Experimental data demonstrating these relationships between temperature and product distribution are presented in graphical form in Figure 1 of the drawing. The data summarized in the curves of Figure 1 were obtained in a 1.6" diameter, dense phase fluid type exploratory unit containing a fluidized bed of sand externally heated. The sand had a particle size of about -180 microns and was fluidized at a linear superficial gas velocity of about 1.5-2.5 ft. per second by injecting the feed together with '75 weight per cent of steam into the bottom of the fluidized bed at atmospheric pressure. The oil feed rate was about 3 w./hr./w. The feed stock used was a 16% West Texas residuum having the inspection given below.

Gravity, API 11 Gonradson carbon, weight per cent 15 Furol viscosity at 210 F., sec 96.6 H/C atomic ratio 1.53

Referring now to Figure 1, the curves shown therein indicate the changes in the yields of total liquid product (Curve I), gas oil (Curve II), gasoline (Curve III), carbon (Curve IV) and gas (Curve V) as a function of temperature variations Within the range of 8501100 F. at otherwise comparable conditions. It will be noted that all the curves show a definite break at a temperature of about 950 F. This break is particularly sharp in Curve II (gas oil) and Curve III (gasoline). More specifically, the curves show that as the temperature rises above 850 F., gasoline and coke yields decrease slightly and the gas oil yield increases markedly while total liquid and gas yields remain about constant, up to the critical temperature of about 950 F. Upon a further rise in the temperature there is a sharp increase in the gasoline yield and a similarly sharp decrease in the gas oil yield. There is a somewhat less pronounced drop in the total liquid product yield and an increase in the gas yield, while the coke yield remains substantially unchanged.

The data illustrated in Figure 1 thus show that when operating in accordance with the invention optimum conversion into gas oil at relatively low carbon make may be accomplished in the first stage by maintaining the temperature close to, but not exceeding, about 950 F., say about 930-950 F., while optimum conversion to gasoline may be obtained in the second stage without any increase in the rate of coke formation by raising the temperature substantially above 950 F. and preferably up to about 1100 F. Appreciably higher temperatures will be conducive to excessive gas formation and a. corresponding loss in total liquid product.

Furthermore, Curves II and III clearly indicate that the increase in the gasoline yield above 950 F. takes place at the expense of gas oil; that is, extensive cracking of gas oil into gasoline and, to a lesser extent, into gas and coke takes place at these higher temperatures. Therefore, the yield of gasoline may be substantially increased by contacting the eflluent from the first stage with the inert solids of the second stage at the higher second stage temperature of, say, about 1000-1100 F., in accordance with a preferred embodiment of the invention. If desired, a gas oil fraction may be first separated from the efiluent of the first stage and returned to the second stage for further cracking.

In many cases, it may be desirable to rapidly cool the effluents of either stage to avoid undesirable side reactions in the disperse phase and subsequent system parts, particularly excessive gas formation and/or carbon deposition at the expense of desirable product vapors. To prevent this, either one or both eliiuents may be quenched by passing the same through a fluidized solids quenching zone, solids entrained from the coking zones serving as contacting agent. Such a quench zone also may serve to strip adhering product from the entrained solids.

Having set forth its objects and general nature, the invention will be best understood from the following, more detailed description of specific examples read with reference to Figures 2 and 3 of the drawing.

Referring now in detail to Figure 2 of the drawing, a heavy oil residue, for example 816% West Texas residuum, may be supplied in the liquid state at a temperature of about 500-600 F. to line i. Steam may be admixed with the feed as a diluent in amounts of about -60 wt. to facilitate liquid flow and subsequent fluidization. The liquid feed in line I is mixed With hot fluidizable solids supplied by standpipe 3 as will appear more clearly hereinafter. The inert solid may, for example, be petroleum coke having a particle size of about 50-200 microns and a temperature of about 1050-1100 F. The feed ratio of solids: oil into line I may be about 6/1-1/1 so as to establish a temperature of the mixture of about 825-950 The mixture then passes through line 5 where a dilute suspension of highly heated petroleum coke in steam or gasiform hydrocarbon may be added from line 1 at a temperature of about 1150-l800 F. if required to raise the temperature of the total mixture to about 900-950 F.

The mixture of oil and coke passes into first stage reactor 9 through .a suitable distributing means, such as perforated plate ll, arranged in the conical bottom of reactor 9. This reactor is so designed that at the prevailing feed conditions, a dense turbulent mass M9 of solids fluidized by the upwardly flowing vapors and gases is formed above grid plate ll. Mass M9 assumes a marked interface or level L9 separating it from an upper disperse phase D9. The apparent density of mass M9 may be about -50 lbs. per cu. ft. The temperature of mass M9 ismaintained at about 900- 950 F. by the sensible heat of the feed supplied thereto. At these conditions, level L9 should be so adjusted that the volume of mass M9 is about to 1 times the volume of liquid residue supplied to line I per hour. Level L9 may be controlled by solids overflow pipe l3 provided with valve ii. If desired, pipe I3 may be adjustable in height. Solids overflow through pipe I3 is preferably so controlled that a solids residence time in reactor 9 of about -5 minutes is provided. At these conditions, about 50-80% of the oil feed is converted into volatile products containing about 75-90 wt. of gas oil, about 8-19 wt. of gasoline and about 2-6 wt. gas. The remainder of the feed remains dispersed on the solids and is withdrawn therewith through pipe 13. Volatile products and diluent vapors may be withdrawn through line H via suitable gas-solids separation means, such as cyclone [9, from which separated solids may be returned to mass M9 via line 2!. The volatile effluent may be passed through line 23 to conventional product recovering equipment including a fractionation zone (not shown).

The coke overflowing through pipe [3 passes into second stage reactor 25. Simultaneously, a dilute suspension of highly heated coke in fiuidizing gas such as steam, gasiform hydrocarbons, etc. is supplied to reactor 25 from line 2'! via distributing means, such as feed cone 29 having a perforated top. The hot solids supplied through cone 29 may have a temperature of about 1150"- 1800 F. as the result of partial combustion of coke as will appear hereinafter. These solids may be fed to reactor 25 in amounts of about 5-40 parts by Weight per weight of residuum feed to maintain the total solids therein at a temperature of about 1050-1l00 F. The steam entering through cone 29 is fed in amounts sufficient to establish within reactor 25 a linear superficial vapor velocity of about 0.3-3 ft. per second suitable to convert the solids in reactor 25 into a dense turbulent mass M25 having an upper level L25 and to form thereabove a disperse phase D25. The apparent density of mass M25 may be about 20-50 lbs. per cu. ft. Solids from mass M25 are Withdrawn through standpipe 3 for circulation in the system and, if desired, through pipe 3! for coke recovery. The solids supply through lines it and 2'! and the solids withdrawal through lines 3 and SI should be so balanced as to provide a solids residence time of at least 5 minutes in reactor 25. Coking of the feed constituents previously deposited on the solids is completed and coke and volatile products are produced amounting to about 7-11 weight percent and 9-43 weight percent on feed, respectively. The volatile products may contain about 30-40 weight percent of gasoline, -40 Weight percent gas oil, and 25-30 Weight percent gas. They may be Withdrawn through line 33 and cyclone 35 to be passed via line 3'? to product recovery. Separated solids may be returned via line 39 to mass M25. A portion of the solids in standpipe 3, which may be aerated and/or stripped through one or more taps t in a conventional manner, is supplied to line I in the manner described above.

The remainder of the solids in standpipe 3 is branched ofi into a similar standpipe 4| which feeds into line 43. Air is supplied to line 43 from line 45 to form a dilute suspension of solids-ingases which is passed through line 43 and feed cone 4'! into a lower portion of burner-heater 49. The air supply is so regulated that a dense turbulent mass of solids M49 having an upper level L49 similar to masses M9 and M25 is maintained in heater 9 at a temperature of about 115()- 1800 F. The gases may be withdrawn overhead from level L49 and passed via cyclone 5i and line 53 to any desired use. Separated solids may be returned to mass M49 via line 55 and make-up solids may be added via line 5 Fluidized solids are withdrawn from heater 45 through standpipe 59 and supplied to line (H in an amount equal to the total amount of solids passed through lines 7 and 27. Fluidizing gas, such as steam or hydrocarbons, is supplied to line 6! from line 83 to form a hot solids-in-gas suspension to be supplied to lines '1 and 2i in the proportions and for the purposes indicated above.

In accordance with a highly desirable modifrcation of the invention, at least a portion of the volatile products in line H may be passed through lines 65 and 27 to second stage reactor 25. In addition or as an alternative to this flow of volatile products, gas oil separated in the fractionator zone of the product recovery system (not shown) may be returned through line 87 and passed via lines 65 and 2'1 to reactor 25 for recracking. In this manner, the gasoline yield may be increased by about 18 to 35 weight percent based on residuum feed.

The system of Figure 2 permits of various modifications. Pipe 13 may be a bottom drawofi line rather than an overflow and volatile products from reactor 25 may be directly passed into a lower or upper portion of reactor 9 as will be understood by those skilled in the art. Other modifications within the spirt of the invention may appear to those skilled in the art.

A system similar to that of Figure 2 is illustrated in Figure 3 in a simplified manner. The system of Figure 3 differs from that described above, chiefly in the provision of a fluidized uenching zone and in the fact that the second stage reactor may be of the upflow type. Elements analogous to those appearing in Figure 2 are identified by like reference numerals.

Referring now in detail to Figure 3, the residual oil feed may be supplied via line i to fluid type, dense phase, first stage reactor 9, heat carrying solids being added via line 3 to establish first stage reaction conditions in reactor 9 in a manner analogous to that described with reference to Figure 2. However, level L9 is maintained in a position close to the top of vessel 9 to reduce disperse phase or outage D9 to a minimum. As a result, the volatile products of reactor 8 enter outlet line ll immediately upon their formation. A quenching medium such as oil, water, wet steam, and/or fluidized inert make-up solids is supplied through line if! and passed together with the product from reactor 9 into a fluid type quenching zone 72 wherein the solids entrained from mass M9 form a dense, turbulent, fluidized mass M72 of the type of mass M9. The temperature of mass M72 is maintained by the quenching agent at abotu 500-800 F. so as to avoid any after-cracking of volatile products. Simultaneously, products adhering on solids entrained from mass M9 are stripped in zone 12 by the quenching agent introduced through line 76. Quenched products may be passed to product recovery via line M. Fluidized solids and non-strippable hydrocarbons and/or residues from mass M72 may be returned to vessel 9 via lines 15, I6, and 3 or to reactor 25 via lines '15, TI and I 3.

Inert solids carrying coke and unconverted feed are withdrawn from reactor 9 via line :3, which is now shown as a bottom drawoff line, and the withdrawn solids are passed to second stage reactor 25. Highly heated solids withdrawn from heater 49 are supplied to reactor 25 via lines 59 and 21, fluidizing gas being added through line 63 to maintain in reactor 25 severe coking conditions of temperature and residence time similar to those described with reference to Figure 2. However, fluidization conditions may be so controlled that a higher percentage of solids may be taken overhead from mass M25 and no bottom drawofi is required. Linear superficial gas velocities of about 1-5 ft. per second are suitable for this purpose for the type and size of the solids here involved.

The suspension of inert solids in second stage products may be passed through line 33 to cyclone separator 35 from which the volatile product may either be passed to recovery via line 31' or preferably to quenching zone 12 via line '56. A portion of the solids separated in separator 35 is passed to line 3' and reactor 9 as described above, while the remainder is passed through line ti to heater 59 to be reheated therein as described with reference to Figure 2.

Most of the modifications described with reference to Figure 2 are equally applicable to the system of Figure 3. Particularly, volatile product from reactor 9 or gas oil recovered therefrom may be supplied to second stage reactor 25 via lines 65 and 6'! in a manner analogous to that described with reference to Figure 2.

The foregoing description and exemplary op erations have served to illustrate specific embodiments of the invention but are not intended to be limiting in scope.

What is claimed is:

1. In the process of producing motor fuels by contacting heavy residual oils with subdivided, catalytically inert solids fluidized by an upflowing gasiform fluidizing medium at coking conditions, the improvement which comprises carrying out said process in two successive stages wherein said oils are contacted with said inert fluidized solids in the first stage at relatively mild cracking corditions including temperatures of about 900-950 conducive to the cracking of only the less refractory constituents of said oils so as to form volatile products and coke and to deposit unconverted, unvaporized oil together with said coke on said solids and wherein said inert solids carrying such deposits of unvaporized oil are withdrawn from said first stage and subjected in a second stage in the fluidized state to relatively severe thermal cracking conditions including temperatures of about 1000-1100 F., said severe cracking temperatures being obtained by directly adding freshly heated inert solids to said second stage in addition to the solids carried over from said first stage to form additional volatile products from said deposited oil and to deposit additional coke on said solids, withdrawing volatile 9 products from said stages and withdrawing cokecarrying solids from said second stage.

2. The process of claim 1 in which in said first stage a solids residence time of about to minutes and in said second stage a solids residence time of at least 5 minutes are maintained.

3. The process of claim 1 in which the volume of fluidized inert solids in said first stage is about A; to the volume of liquid residual oil supplied to said first stage per hour.

4. In the process of producing motor fuels by contacting heavy residual oils with subdivided catalytically inert solids fluidized in a coking zone by an upwardly flowing gasifo'rm medium at coking conditions, wherein heat is supplied to said coking zone by circulating coked solids from said coking zone to a fluid type combustion zone and returning solids highly heated in said combustion zone to said coking zone, the improvement which comprises contacting said oils with said solids in. a first fluid type coking zone at relatively mild coking conditions including temperatures of about 900-950 F. conducive to the cracking of only the less refractory constituents of said oils so as to form volatile products and coke and to deposit unconverted, unvaporized oil together with said coke on said solids, passing solids carrying such deposits of unvaporized oil from said first stage to a second fluid type coking stage, subjecting said solids in said second stage in the fluidized state to relatively severe coking conditions including temperatures of about 1000-1100 F. by adding to said second stage freshly heated inert solids in addition to those carried over from said first stage so as to form additional volatile products from said deposited oil and to deposit additional coke on said solids, returning part of the solids from said second stage to said first stage to supply heat to the latter, passing another part of the solids from said second stage to said fluid type combustion zone, returning solids highly heated in said combustion zone to said second stage as aforesaid to supply heat thereto, and withdrawing volatile products from both said stages.

5. The process of claim 4 wherein in said first and second stages residence times of about to 5 minutes and at least 5 minutes, respectively, are maintained.

6. The process of claim 4 in which a gas oil fraction recovered from said Withdrawn products is recycled to said second stage.

7. The process of claim 4 in which at least a portion of the volatile product withdrawn from said first stage is passed to said second stage.

8. The process of claim 4 in which said withdrawn volatile products are quenched in a fluid solids quenching zone to a temperature below incipient cracking of the products.

9. In the process of producing motor fuels by contacting heavy residual oils with subdivided, catalytically inert solids fluidized by an upflowing gasiform fluidizing medium at coking conditions, the improvement which comprises carrying out said process in two stages wherein said oils are contacted with said fluidized inert solids in the first stage at relatively mild cracking conditions including temperatures of about 900-950 F. conducive to the cracking of only the less refractory constituents of said oils so as to form volatile 10 products and coke and to deposit unconverted, unvaporized oil together with said coke on said solids and wherein solids carrying such deposits of unvaporized oil are withdrawn from said first stage and subjected in a second stage in the fluidized state to relatively sever thermal cracking conditions including temperatures of about 1000-1100 F. by introducing into said second stage additional freshly heated inert solids at higher temperature than the solids from said first stage to form additional volatile products from said deposited oil and to deposit additional coke on said solids, withdrawing volatile products from both of said stages, Withdrawing coke-carrying solids from said second stage and contacting gas oil constituents of the volatile products withdrawn from said first stage with the fluidized solids in said second stage.

10. In the process of producing motor fuels by contacting heavy residual oils with subdivided catalytically inert solids fluidized in a coking zone by an upwardly flowing gasiform medium at coking conditions, wherein heat is supplied to said coking zone by circulating coked solids from said coking zone to a fluid type combustion zone and returning solids highly heated in said combustion zone to said coking zone, the improvement which comprises contacting said oils with said solids in a first fluid type coking zone at relatively mild coking conditions including temperatures of about 900950 F, conducive to the cracking of only the less refractory constituents of said oils so as to form volatile products and coke and to deposit unconverted, unvaporized oil together with said coke on said solids, passing solids carrying such deposits of unvaporized oil from said first stage to a second fluid type coking stage, subjecting said solids in said second stage in the fluidized state to relatively severe coking conditions including temperatures of about 1000-1100 F. so as to form additional Volatile products from said deposited oil and to deposit additional coke on said solids, returning solids from said second stage to said first stage to supply heat to the latter, passing solids from said second stage to said fluid type combustion zone, returning solids highly heated in said combustion zone to said second stage to supply heat thereto, withdrawing volatile products from both of said stages, contacting gas oil constituents of the volatile products withdrawn from said first stage with the fluidized solids in said second stage, and passing the total vapor products through a cooling zone to reduce their temperature to within the range of 500 to 800 F. and thereby quench further reaction of said products.

11. The process of claim 10 in which solids highly heated in said combustion zone are passed directly to said first stage to supply additional heat thereto.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,388,055 Hemminger Oct. 30, 1945 2,436,160 Blanding Feb. 17, 1948 2,436,486 Scheineman Feb. 24, 19 18 2,444,131 Delattrc-Seguy June 29, 1948 2,573,906 Hufi Nov. 6, 1951 

1. IN THE PROCESS OF PRODUCING MOTOR FUELS BY CONTACTING HEAVY RESIDUAL OILS WITH SUBDIVIDED, CATALYTICALLY INERT SOLIDS FLUIDIZED BY AN UPFLOWING GASIFORM FLUIDIZING MEDIUM AT COKING CONDITIONS, THE IMPROVEMENT WHICH COMPRISES CARRYING OUT SAID PROCESS IN TWO SUCCESSIVE STAGES WHEREIN SAID OILS ARE CONTACTED WITH SAID INERT FLUIDIZED SOLIDS IN THE FIRST STAGE AT RELATIVELY MILD CRACKING CONDITIONS INCLUDING TEMPERATURE OF ABOUT 900*-950* F. CONDUCIVE TO THE CRACKING OF ONLY THE LESS REFRACTORY CONSTITUENTS OF SAID OILS SO AS TO FORM VOLATILE PRODUCTS AND COKE AND TO DEPOSIT UNCONVERTED, UNVAPORIZED OIL TOGETHER WITH SAID COKE ON SAID SOLIDS AND WHEREIN SAID INLET SOLIDS CARRYING SUCH DEPOSITS OF UNVAPORIZED OIL ARE WITHDRAWN FROM SAID FIRST STAGE AND SUBJECTED IN A SECOND STAGE IN THE FLUIDIZED STATE TO RELATIVELY SEVERE THERMAL CRACKING CONDITIONS INCLUDING TEMPERATURES FO ABOUT 1000*-1100* F., SAID SEVERE CRACKING TEMPERATURES BEING OBTAINED BY DIRECTLY ADDING FRESHLY HEATED INERT SOLIDS TO SAID SECOND STAGE IN ADDITION TO THE SOLIDS CARRIED OVER FROM SAID FIRST STAGE TO FORM ADDITIONAL VOLATILE PRODUCTS FROM SAID DEPOSITED OIL AND TO DEPOSIT ADDITIONAL COKE ON SAID SOLIDS, WITHDRAWING VOLATILE PRODUCTS FROM SAID STAGES AND WITHDRAWING COKECARRYING SOLIDS FROM SAID SECOND STAGE. 